1. Field of the Invention
The present invention relates to a novel substance, a crystalline 2-O-.alpha.-D-glucopyranosyl-L-ascorbic acid, and its preparation and uses.
2. Description of the Prior Art
L-Ascorbic acid, which has the chemical structure shown by the formula [I]: ##STR1## is not synthesized in vivo in human, monkey and guinea pig, and therefore is listed as an essential nutritive element, i.e. vitamin C.
L-Ascorbic acid takes part in some physiological activities in vivo; for example, in the hydroxylation of proline and lysine which are necessary to synthesize collagen as the main element of living connective tissues; the oxidation-reduction reaction of cytochrome C wherein Fe.sup.+++ is reduced into Fe.sup.++ ; and in immunopotentiation via the increase of leukocytes. Thus vitamin C plays a significant role in the maintenance and promotion of health in living body.
Scurvy has been known long as a condition due to a deficiency of L-ascorbic acid, and is marked by weakness of the skin, petechial hemorrhage, ecchymosis, and hemorrhages in the gingiva and marrow. To prevent scurvy for the maintenance of health, a recommended daily administration (RDA) is established for L-ascorbic acid; in particular, 60 mg for adult males and 50 mg for adult females.
Nowadays the use of L-ascorbic acid is not limited to agents which enrich vitamin C as an essential nutritive element, but is extending to various applications. More particularly, because of its chemical structure and physiological activities, L-ascorbic acid is useful as a souring agent, reductant, antioxidant, bleaching agent and stabilizer in various chemical reagents, foods and beverages; in pharmaceuticals against susceptive diseases such as prevention and treatment for viral diseases, bacterial diseases and malignant tumors; and further as a reductant, uv-absorbent and melanin-formation inhibitor in cosmetics including skin-refining agent and skin-whitening agent.
The major drawback of L-ascorbic acid is that it readily loses its physiological activities because of its direct reducing activity, poor stability and high susceptibility to oxidation.
To stabilize L-ascorbic acid, some saccharide derivatives of L-ascorbic acid have been proposed. For example, we disclosed in Vitamin, Vol. 43, pp. 205-209 (1971), ibid., Vol. 47, pp. 259-267 (1973), and Japanese Patent Publication No. 38,158/73 a biochemical synthesis of L-ascorbic acid glucosides.
Because of the facts that the glucosides are prepared by similar methods; that the formation of an ether bond at the primary alcohol group which is located at the number six carbon atom in L-ascorbic acid leads to the glucosides as described in the Japanese Patent Publication, for example, on the 2nd column, lines 14-16; that the saccharide-transfer reaction from maltose to an .alpha.-glucosyl group is responsible for the formation of glucosides; and that the glucosides exhibit a direct reducing activity, their chemical structure would be shown by the formula [II]: ##STR2##
As obvious from the results in the Japanese Patent Publication, the table in Example 1, the stability of the glucosides is superior to that of L-ascorbic acid, but is not enough for their commercialization.
Ishido et al. disclose in Japanese Patent Publication No. 5,920/83 an organic chemical process to synthesize saccharide derivatives of L-ascorbic acid.
These derivatives are, however, those wherein all the D-glucoses are bound in the .beta.-fashion because up to 21 .beta.-D-glucopyranosyl type derivatives of L-ascorbic acid including 2,3-di-O-(.beta.-D-glucopyranosyl)-L-ascorbic acid are listed for explanation on the 7th column, line 6 to the 8th column, line 11.
Masamoto et al. disclose in Japanese Patent Publication No. 198,498/83 an organic chemical process to synthesize saccharide derivatives of L-ascorbic acid which are also of the .beta.-glucosyl type.
Studies on the .beta.-D-glucopyranosyl type derivatives of L-ascorbic acid confirmed that they hardly exhibit desired physiological activities in living body, especially in humans. Furthermore, conventional organic chemical processes have the drawbacks that they are inferior in economical efficiency because the reaction is very complicated and low in yield, and the establishment of non-toxicity and safeness for the resultant derivatives is very difficult.
As described above, the proposals of saccharide derivatives of L-ascorbic acid in the prior art have proved unsatisfactory in view of stability, safeness, physiological activity and economical efficiency, and not been practiced hitherto.
The present invention has as an object to overcome the drawbacks of conventional saccharide derivatives of L-ascorbic acid. More particularly, we studied a novel saccharide derivative of L-ascorbic acid which is obtainable by a biochemical process utilizing a saccharide-transfer reaction.
As disclosed in the specification of Japanese Patent Application No. 127,072/89, we discovered a novel substance, an .alpha.-glycosyl-L-ascorbic acid, especially, 2-O-.alpha.-D-glucopyranosyl-L-ascorbic acid, which is free from direct reducing activity, superiorly stable, readily hydrolyzable in vivo, and satisfactorily high in physiological activity, as well as developing its preparation and uses in foods, beverages, pharmaceuticals for susceptive diseases, and cosmetics.
It was also found that since, when L-ascorbic acid is ingested with an .alpha.-glucosyl saccharide, 2-O-.alpha.-D-glucopyranosyl-L-ascorbic acid is synthesized and then metabolized in vivo, it would be an ideally convenient, novel saccharide derivative of L-ascorbic acid in view of its safety.
A powder which is obtainable by concentrating and pulverizing an aqueous solution of 2-O-.alpha.-D-glucopyranosyl-L-ascorbic acid is amorphous and strongly hygroscopic, and has the drawback that it readily absorbs moisture under ambient conditions to cause deliquescence and consolidation.